(1) Field of the Invention:
The present invention generally appertains to improvements in structural concrete forming and especially relates to new and novel improvements in devices for forming or producing openings or bores in concrete slabs, such as floors, ceilings or the like, during the pouring and setting of the concrete.
(2) State of the Prior Art:
The use of reinforced concrete slabs in the construction of buildings has increased to the point that time and expense are important in the pouring thereof and in the installation of pipes, electrical conduits and the like therein after they are set. It is no longer practical or feasible to drill passages or openings in the cured concrete. Thus, present commercial practice dictates that the openings for the pipes, conduits and the like be produced when the concrete is poured.
Many forms or sleeves are to be found in the prior art for accomplishing the production of such openings.
Thus, as early as 1931 an impractical attempt was made in U.S. Pat. No. 1,801,346 but the use of an envelope of textile material stuffed with a sand filler was not feasible.
In U.S. Pat. No. 3,265,349, a longitudinally split sheet metal sleeve is disclosed with the sleeve being adjustable by means connecting its split edges so that it could assume differing diameters.
In U.S. Pat. No. 3,346,230, a telescopic plastic sleeve is disclosed.
In U.S. Pat. No. 3,758,068, a form for molding a tapered bore in concrete is disclosed.
In U.S. Pat. No. 4,077,599, an elongated tubular body is provided with engaging means so as to frictionally secure it in a form holder.
In all instances, except in one impractical embodiment in U.S. Pat. No. 1,801,346, the bore or passageway produced in the slab is straight. This is satisfactory, in some instances, for the movement of pipes or conduits through a slab. But, in many instances difficulties can be faced, For example, in the instance of passing an electrical conduit through a bore or passage in a concrete floor slab--which has been produced by one or the known straight tubular forms to result in a straight tubular bore or passage--it necessitates bending the conduit in a goose-neck design form below the floor slab so as to align the leading end portion of the conduit with the straight axis of the bore.